1. Field of the Invention
This invention relates to an air-cooled motor having cooling-air passages formed through a front housing, a stator, and a rear housing, which are constructed in one piece, the cooling-air passages each being formed by a plurality of small ventilation passages.
2. Description of the Related Art
Conventionally, an air-cooled motor is known, which includes a stator, and a front housing and a rear housing provided on opposite sides of the stator, all constructed in one piece, with the front housing, the stator, and the rear housing being formed with cooling-air passages which extend therethrough and are each formed by a plurality of small ventilation passages. The construction of cooling-air passages of an air-cooled motor of this type will be described below with reference to FIG. 5 and FIG. 6.
FIG. 5 (PRIOR ART) shows a front of a conventional air-cooled motor. In the figure, reference numeral 50 designates a front housing provided on a front side of the air-cooled motor, which is followed on the reverse side of the figure by a stator and a rear housing, not shown in this figure, which are constructed in one piece with the front housing 50. The front housing 50 has a fixture flange 51 formed on a front side thereof, which provides a motor-fixing end face via which the motor is fixed to a partner machine to be associated therewith. The fixture flange 51 is constructed such that an annular projection 52 thereof fits into a fitting opening of the partner machine. The annular projection 52 includes a large number of radial ribs 52a, as shown in the figure, for reinforcement thereof. Further, the fixture flange 51 has bolt holes 53 formed therethrough at four corners thereof for bolting the motor to the partner machine. A shaft 600 extending from the center of the stator projects out of the front end face of the motor, and a shaft cover 54 is provided such that it surrounds the shaft 600, and closes space between the shaft 600 and the annular projection 52.
The front housing 50 has cooling-air inlet ports 55 formed therein by cutting out four corners thereof, respectively. Front and rear walls defining the cooling-air inlet 55 ports are formed by the fixture flange 51 of the front housing 50 and a joining flange 57 forming a joint with the stator, respectively. Each of the cooling-air inlet ports 55 is connected to a cooling-air passage 56. The cooling-air passage 56 is provided for cooling the stator by cooling air caused to flow therethrough, and extends through the joining flange 57 of the front housing 50, the stator, and the rear housing. The construction of the cooling-air passage 56 will be described with reference to FIG. 6.
FIG. 6 (PRIOR ART) is a cross-sectional view taken on line B--B of FIG. 5. In the figure, the cooling-air passage 56 is formed by a plurality of (six, in this example) small ventilation passages 56a. Each of the small ventilation passages 56a is defined between adjacent ones of seven ribs 611, 612, 613, 614, 615, 616, and 617, each rib forming part of the stator. The ribs 611 and so forth are formed by a laminate 62 of rib-shaped portions of flat rolled magnetic steel sheets. Out of the seven ribs 611 and so forth, alternate ones 611, 613, 615, and 617 are additionally formed with front housing ribs 501, 502, 503, and 504 on the cooling-air inlet side thereof, so that the cooling-air passage 56 has three wide inlets 56b on the cooling-air inlet side, each of which is bifurcated into two narrow inlets 56c each formed by a small ventilation passage 56a. The front housing ribs 501 and so forth each form a part of the joining flange 57.
In the cooling-air passage 56 constructed as above, cooling air flows into the wide inlets 56b in the direction of an arrow 80, and then into the narrow inlets 56c bifurcated from each of the wide inlets 56b, followed by flowing through the stator.
In the case of the cooling-air passage 56 constructed as above, the narrow inlets 56c are not identical in position or height with the wide inlets 56b. Therefore, if cuttings are contained in the cooling air, the cuttings are liable to be caught by stepped shoulders 56d which divide the wide inlets 56b into the narrow inlets 56c, and are gradually accumulated thereon. As a result, there are formed layers 70 of accumulated cuttings which would eventually clog the small ventilation passages 56a. When a small ventilation passage 56a is clogged with a layer 70 of accumulated cuttings, cooling air cannot flow therethrough any longer, which results in a lowered cooling capability of the cooling-air passage 56.